1) Field of the Invention
The invention relates to low pressure mercury vapor fluorescent lamps.
2) Description of the Prior Art
Lighting accounts for approximately 20-25% of the electricity used annually in the United States. For stores, offices and warehouses, lighting may account for up to 50% of their electrical consumption. The Environmental Protection Agency (EPA), through its Green Lights program, encourages commercial, industrial and public facilities to switch to energy efficient lighting. Efficient lighting reduces the need for electric power generated through the burning of fossil fuels and the harmful air pollutants generated thereby.
Low pressure mercury vapor lamps, more commonly known as fluorescent lamps, are a key element in the Green Lights Program. These lamps have a lamp envelope with a filling of mercury and a rare gas and in which a gas discharge is maintained during lamp operation. The radiation emitted by the gas discharge is mostly in the ultraviolet region of the spectrum, with only a small portion in the visible spectrum. The inner surface of the lamp envelope has a luminescent coating, often of a blend of phosphors, which emits visible light when impinged by the ultraviolet radiation.
While the use of fluorescent lamps was being promoted during the late 1980's and early 1990's, there was also growing concern about the disposal of an ever-increasing number of these lamps, due to their mercury content. In 1990 the Environmental Protection Agency (EPA) established the Toxicity Characteristic Leaching Procedure (TCLP) test, which created additional challenges for manufacturers and users of fluorescent lamps. The TCLP test simulates the leaching effects of mildly acidic rainwater in landfills on solid waste. The test procedure is set forth at pages 26,987-26,998 of volume 55, number 126 of the Jun. 29, 1990 issue of the Federal Register (herein incorporated by reference). The lamp being tested is pulverized into granules having a surface area per gram of materials equal to or greater than 3.1 cm.sup.2 or having a particle size smaller than 1 cm in its narrowest dimension. The granules are then subject to a sodium acetate buffer solution having a PH of approximately 4.9 and a weight twenty times that of the granules. The buffer solution is then extracted and the concentration of mercury is measured. In order for fluorescent lamps to be considered non-hazardous and lawfully disposable in landfills (the cheapest option), the lamps must pass the TCLP test for mercury by meeting a regulatory threshold of 0.2 mg per liter (0.2 ppm) in the leachate.
Disposal of fluorescent lamps is therefore a serious issue for most industrial/commercial facilities. Hazardous waste regulation means that large office buildings and other typically non-hazardous manufacturing facilities are now subject to all of the requirements of a hazardous waste generator. In response to these concerns, a recycling/reclamation industry has established itself in the United States for fluorescent lamps, but at a substantial cost to end users. Recycling facilities gather the mercury from fluorescent lamps by retorting, selling the aluminum bases, and finding various uses for the glass. Some facilities are run as Subtitle C (hazardous waste) facilities. Disposal at non-Subtitle C facilities is approximately seven to twelve cents per foot ($0.28 to $0.50 for a 4 ft. lamp) and at a Subtitle C facility is $1.00 to $1.50 for each 4 ft. lamp.
U.S. Pat. Nos. 5,229,686 and 5,229,687 (both to Fowler et al) disclose two techniques for reducing the soluble mercury extracted in the TCLP test. The lamp is provided with an agent for chemically removing a substantial quantity of the soluble mercury when the lamp is pulverized to granules and subjected to the TCLP buffer solution. The '686 patent discloses the use of various salts, such as potassium periodate, which tie up the mercury ions as an insoluble mercury compound. The '687 patent discloses the use of metals having an oxidation potential higher than mercury, such as iron, tin and copper, which reduce the mercury ions to elemental Hg, which is only sparingly soluble and is detected at only a very low level by the test. These agents are provided in a container in the lamp or lamp cap to be pulverized along with the lamp.